Over-current and under-current protective switch



Dec. 2, 1947.

F. J. PAVITT 2,431,886 ND UNDER-CURRENT PROTECTIVE ySWITCH OVER-CURRENT A Filed May 29, 1942 3 Sheets-Sheet l TRIP AMPS TRIP AMPS TRIP AMPS F. J. PAvn-T 2,431,886

-CURRENT PROTECTIVE SWITCH Dec. 2, 19471 3 Sheets-Sheet 2 OVERCURRENT AND UNDER Filed May 29, 1942 NvEiNTol? Dec. 2, 1947.

l OVER-CURRENT AN F. J; PAvxT'r 2,431,886

D UNDER-CURRENT PROTECTIVE SWITCH Filied May 29, 1942 s sheets-sheet s 25 4e v t 29 .2 i *30 i 28 29/ f 2 INVNTOR Pavzlf,

ATTORN Y Patented Dec. 2, 1947 UNITED STATES PATENT OFFICE OVER- CURRENT AND PROTECTIVE UNDER- CURRENT SWITCH Frederick James Pavitt, Brighton 7, England Application May 29, 1942,

In Great Serial No. 444,998

Britain June 13, 1941 15 Claims. (Cl. 175`294) Other objects and advantages will appear hereinafter.

The invention consists broadly in the arrangement that a common winding operates both as an over-current and as an under-current or novolt winding. n

In order that the invention may be the more clearly un being made to the accompanying drawings, wherein:

Figure 1 is a front elevation of said starter.

Figure 2 is a plan of the same shown partly in section.

Figure 3 is a sectional side elevation of the same taken on the line X-X of Figure 2.

Figure 4 is a sectional side elevation ofthe saine taken on the line Y-Y of Figure 2.

Figure 5 is a front elevation of partly in section on the line Z-Z Figure 6 is nections.

Referring to the drawings, the three phase motor starter comprises three vertical coils I adapted to be connected in the three phases of the motor circuit and to act both as under-current coils and as over-current coils.

The circuit of a motor M is completed through the same shown of Figure 2. a diagram showing the circuit conrence of either over-current or under-current are adapted to deenergise said winding 1 by disengaging a pair of contacts 8 which are connected for starting and stopping the motor under normal conditions.

In order that the coils I shall function as stated both as over-current coils and as under-current said coils has an under-current arupwardly by means of a spring I0 attracted position, an over-current plunger II within the coil adapted to be moved upwardly upon the occurrence of over-current, and an acthe under-current armature 9 or of the overcurrent plunger II.

Said actuating rod I 2 is located vertically within the upper portion of the coil I above the overcurrent plunger II.

mature, as shown in Figure 2, and is formed with der-current armature 9 at the down or position this enlarged head I4 rests Should over-current conditions occur the overactuating rod I2 independently of the under-curto the actuating position, and should under-current occur, the under-current armature 9 will rise under the influence of its spring I0 to the non-attracted position, thereby lifting said actuating rod I2 independently of said over-current plunger. Each coil I has a and extending throughout its entire length. The

tube portion of the core I5 is prevented.

Each under-current armature 9 takes the form of a pivotedplate which at shown is horizontal and flush against the upper end of the core I5, and at the non-attracted position is upwardly tilted. The opening I3 therein for the actuating rod l2 takes the form of a slot as shown, bifurcating said armature at right angles to its axis of oscillation. One of the prongs of bifurcation has mounted upon it a silencing coil l1 in the form of a single turn of copper strip.

The pivotal mounting of each under-current armature is effected by providing it with an eX- tending lug I8 which passes through an opening in a fined vertical plate I9 located alongside the respective coil l. Each aforesaid spring iii for biasing the respective under-current armature to the non-attracted position is a tension spring and is secured at one end to the lug i8 and at the other end to the bottom end of the plate i3.

The plate 9 is of magnetic material and is of about the same length as the core it' and it will be appreciated that, ywith said core extended completely through the coil l as described, said core together with the plate i9 and the armature 9 forms a fairly eiicient magnetic circuit, This is important as the release under-currents must be of the order of to 25% of the full load current of the motor. At the same time the arrangement gives a fairly wide range of adjustment for the over-current settings.

The over-current plunger ll at its lower end carries the plunger 20 of a dash pot 2l whereby the upward movement of said over-ciirrent plunger is retarded. Thus, actuation will not take place in response to a momentary over-current unless this is of very great intensity,

The opening of the contacts 8 in response to the lifting of any or all of the rods l2 is effected through the medium of an actuating plate 22. This actuating plate 22 o-verlies, and normally rests on, the heads lil of the actuating rods I2, and it has an extension 23 which lies underneath one of the contacts 8, (Figure 2,) so that when any or all of the actuating rods l2 are lifted said actuating plate 22 is lifted and thereby lifts the said contact 8 out of engagement with its neigh- Said actuating plate 22 is pivotally top of the Jthree plates i9 each of which has a reduced lug 24 at its upper end which extends through an opening in said actuating plate. as shown in Figure 4, to provide such pivotal mounting.

In order that the actuating rods l2 and actuating plate 22 shall not be lifted by the undercurrent armatures 3 while the coils l are deenergised owing to the starter not being in operation, said actuating plate 22 is positively held at the down position, with sufficient force to prevail over the springs l0, so long as the main bridging contacts 2 are down, and subsequently to said main bridging contacts being listed to the closed position and thereby energising the coils l, said actuating plate 22 is released for response to over-current or under-current as described. To this end two levers 25 are provided pivotally mounted about horizontal axes at 26 and downwardly biased by'means of springs 21 so that their extremities normally bear down upon the actuating plate 22, as shown in Figure 3, and thereby hold it at the attracted position. rl"he lifting of the bridging contacts 2 is effected through the medium of a common contact carrier 28 upon which said contacts are mounted by means of springs 29, and, after said bridging contacts have bridged their stationary contacts 4 and 5, said contact carrier 28 continues to move upwards, as permitted by said springs 29, until upward projections 30 thereon engage said levers 25 and lift them clear of the actuating plate 22. For lifting the Contact carrier 28 upon enwinding 1 is provided with an upper stationary E-shaped magnet frame 3l and a corresponding lower movable E-shaped magnet frame 32. Said lower magnet frame 32 is linked to said contact carrier 28 by means of links 33, and when, upon energisation of the winding 1, said lower magnet frame 32 is attracted upwards to said upper magnet frame 3l said Contact carrier is also lifted.

The aforesaid manually operated switch means for starting and stopping the motor under normal conditions comprise a normally open start push button switch 34 and a normally closed stop push button switch 35 both in series with the winding 1 and the contacts 8. One of the levers 25 carriers a contact 36 which, when said lever is lifted engages a xed contact 31. These contacts 3B, 31 are connected in parallel with the start push button switch 34 and thus operate to maintain the winding 1 energised after momentary depression of the start push button switch has initiated its energisation. Momentary depression of the stop push button switch 35, or momentary opening of the contacts 8 by overcurrent or under-current conditions, will then terminate the energisation of said winding 1 and open the bridging contacts 2 and said winding 1 can only be again energised by depression of the start push button switch 34. It should be noted that, when the circuit breaker is tripped, contacts 36, 31 will open before the levers 25 reclose the contacts 8.

It is obvious that in place of the push button, 34, a simple contacting device could be provided on the unit structure itself for momentarily closing the circuit of the winding 1, and that, in place of the stop push button 35, means could be provided for momentarily opening the contacts 8. Again the arrangement could be such that contacts equivalent to the contacts 8 are normally latched at the closed position, and are unlatched when the actuating plate 22 is lifted, and a single reset-and-stop member adapted to return said contacts to the latched position could, when moved beyond the latched position, be adapted momentarily to open said contacts for de-energising the winding 1 and stoppingr the motor.

The dash pots 2| claimed in prior British may be as described and Specification No. 461,900 modified according to prior British Specification No. 480,805. That is to say, the bobbin 38 of each winding I is made of moulded insulating material and so also is the dash pot cylinder 2l save for a metal lining 39. Said dash pot cylinder is in screwed relation on an extension of said bobbin as shown so that it is axially adjustable relative to the coil l for varying the position of the over-current plunger il .within said coil and therefore the degree of over-current at which said plunger will respond. Also a stationary calibrated plate 40 is mounted alongside each dash pot cylinder so that said position of said cylinder can be read against said plate in terms of the amperes required to effect tripping.

Also, as in said prior British Specification No. 480,805, the dash pot plunger 2B has a hole in it and a dished washer 4l rests on said plunger, said dished washer being adapted to tilt in the event of a heavy over-current and close said hole so that the plunger rises at a rate determined by the clearance surrounding it. In the case of a very severe o-ver-current the plunger of course rises substantially instantaneously. Again, as in prior British Specification No. 480,805, in order that the effective size of the hole in the plunger can be adjusted a hat washer 42 is interposed between the plunger 2i] and the dished washer 4|, said flat washer having a number of holes in it of dilerent sizes and being angularly adjustable around the stem 43 and the hole in the flat Washer 42 are hexagonal so that the flat washer will remain in any of six adjusted positions. The stem 43 is reduced at 44 so that the flat washer 42 may be raised and turned for adjusting it.

With regard to the constructional details of the starter, the parts heretofore described are all supported and united by means of a frame of inwhose somewhat complicated form is deemed sufliciently clear from the drawings. It will be seen that this frame embodies partitions 45 which shroud the three bridging contacts 2 from one another and from the levers 25. The contact carrier 28 also is of insulating material and is formed with rectangular loop like portions 46 which embrace the bridging contacts 2 as shown and serve to limit their upward movement relative to said contact carrier.

Other structural details are deemed clear from the drawings.

What I claim and desire to secure by Letters Patent is:

1. A circuit protecting device for a three phase alternating current circuit comprisingr three coils connected respectively in the three phases, overcurrent armatures associated respectively with said coils and adapted to move to an attracted position upon occurrence of over-current conditions in the respective phases, under-current armatures associated respectively With said coils and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in the respective phases, a circuit interrupter connected in the circuit of two of the three phases, a member extending relative to the three coils and adapted to actuate the circuit interrupter to circuit opening position by the movement of any one of said over-current armatures to its attracted position and by the movement of any one of said under-current armatures to its non-attracted position, and means normally positioned to engage and prevent actuation of said member and retain all three of said under-current armatures in attracted position despite the deenergization of the coils.

2. A circuit protecting device comprising a coil connected in the circuit to be protected, an overcurrent armature associated with said coil and suii'iciently adapted to move toan attracted position upon occurrence of over-current conditions in the coil, an under-current armature associated with the coil and yieldingly urged to a, non-attracted position upon occurrence of under-current conditions in the coil, an electromagnetically actuated switch having its contacts connected in the circuit to be protected and its actuating coil connected in a local circuit, a circuit interrupter connected in said local circuit and normally assuming circuit closing position and causing actuation of the switch to circuit closing position, means operative to actuate said circuit interrupter to circuit opening position and arranged to be operated by the movement of the over-current armature to its attracted position and by the movement of the under-current armature to its non-attracted position to actuate the circuit interrupter to circuit opening position and cause the switch to assume circuit opening position, and means normally positioned to engage and prevent operation of the circuit interruptor actuating means and retain the under-current armature in its attracted position despite the deenergization of the coil when the circuit is open.

3. A circuit protecting device comprising a coil connected in the circuit to be protected, an overcurrent armature associated with the coil and adapted to move to an attracted position upon occurrence of over-current conditions in the coil, an under-current armature associated with the coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in the coil, a circuit interrupter connected in a local circuit and normally in circuit closing position, means operative to actuate the circuit interrupter to circuit opening position by the movement of the over-current armature to ater and adapted to actuate the switch to circuit closing position upon energization thereof, means for actuating said switch to circuit opening position upon de-energization of the electromagnet, and means actuated by the switch opening means to retain the under-current armature in attracted position when the switch is in circuit opening position despite the de-energization of the coil.

fi. A circuit protecting device comprising a coil connected in the circuit to be protected, an overcurrent armature associated with the coil and' adapted to move to an attracted position upon occurrence of over-current conditions in the coil, an under-current armature associated with the coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in the coil, a circuit interruptor connected in a local circuit and normally in circuit closing position, means operative to actuate the circuit interrupter to circuit opening position and arranged to be operated by the movement of the over-current armature to attracted position and by the movement of the under-current armature to nonattracted position rupter to circuit opening position, a switch having its contacts connected in the circuit to be protected, an electromagnet connected in the local circuit of the circuit interrupter and having a movable core member connected to the switch and adapted upon de-energization of the electromagnet by the opening of the local circuit to effect opening of said switch, and means normally positioned to engage and retain the circuit interrupter actuating means in inoperative position and actuated to position out of engagement with the circuit interrupter actuating means by the circuit closing movement of the switch wheretion prevents actuating of the circuit interruptor to circuit opening position despite the de-energization of the coil.

5. A circuit protecting device comprising a coil connected in the circuit t0 be protected, an vovercurrent armature associated with the coil and adapted to move to an attracted position upon occurrence of over-current conditions in the coil, an under-current armature associated with said coil and yieldingly urged to a non-attracted poto actuate the circuit inter-y sition upon occurrence of under-current conditions in the coil, a circuit interrupter connected in a local circuit and normally in lcircuit closing position, means operative to actuate the circuit interrupter to circuit opening position by the movement of the over-current 'armature to attracted position and by the movement of the under-current armature to non-attracted posi-- tion, a switch having its contacts lconnected in said circuit to be protected, an electromagnet connected in the local circuit of the circuit interrupter and having a nected to the switch and adapted upon de-energization of the electromagnet by the opening of the local circuit to effect opening of the switch, auxiliary maintaining contacts yieldingly urged to circuit opening .position 'and actuated to circuit closing position 'by the circuit closing movement of the switch, said auxiliary maintaining contacts being connected in the local circuit to maintain energization of the electrom'agnet after the initial energization of the electromagnet, and means normally engaging the circuit interrupter actuating means to prevent actuation of the circuit interrupter to circuit opening position and operated by the movement of the switch to circuit closing position out of engagement with the circuit interrupter actuating means to permit actuation of the circuit interrupter to circuit opening position.

6. A circuit protec'stingr device comprising a coil connected in the circuit to be protected, an overcurrent armature associated with the coil and adapted to move to an attracted position upon occurrence of over-current conditions in said circuit, an under-current armature associated with the coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in said circuit, a switch having its contacts connected in the circuit to be protected, an electromagnet connected in a local circuit and having a movable core member connected to the switch and adapted upon de-en'ergization of the electromagnet to effect opening lof the switch, a circuit interrupter connected in the local circuit of the electromagnet and normally closing said circuit and adapted to be actuated to' circuit opening position upon movement of the over-current armature to attracted position and upon movement of `the under-current armature to non-attracted position, and auxiliary maintaining contacts yieldingly urged to circuit opening position and actuated to circuit closing position by the circuit closing movement of the switch, said auX- iliary maintaining contacts being connected in the local circuit of the electromagnet to maintain energization of the electromagnet aiter the initial energization of the electromagnet.

7. A circuit protecting device comprising a coil connected in the circuit to be protected, an overcurrent armature associated with the coil and adapted to move to an attracted position upon occurrence of over-current conditions in the coil, an under-current armature associated with the C011 and yeldincly urged to a non-attracted position upon occurrence of under-current conditions in the coil, a circuit interrupter connected in 'a local circuit and normally in circuit closing position and adapted to be actuated to circuit opening position upon movement of the over-current armature to attracted position and upon movement of the under-current armature to non-attracted position, a switch having its contacts connected in the circuit to be protected, an electromagnet connected in the local circuit of the cirmov'able 'core member con-` cuit interrupter and having 'a mov-able core member connected to "the switch and adapted upon de-energization of the electromagnet to effect opening of the switch, and a mechanical interlock actuated by the opening of the switch through the de-energization of the electromagnet to `hold the under-current armature at attracted position.

8. A circuit protecting device comprising a coil connected in the circuit to be protected, an overvcurrent armature associated with the coil and adapted to move to an attracted position upon occurrence of over-current conditions in said circuit, an under-current armature associated with the coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in said circuit, a switch having its contacts connected in said circuit to be protected, an electromagnet connected in a local circuit and having 'a movable core member connected to the switch and adapted upon de-energization of the ele'ctromagnet to eiect opening of the switch, a 'circuit interrupter connected in the local circuit of the electromagnet and normally in circuit closing position, means to actuate the circuit interrupter 'to circuit opening position operative by movement of the over-current armature to attracted position and by the movement of the under-current armature to non-attracted position, auxiliary maintaining contacts connected in the local circuit of the electromagnet and normally in circuit opening position and actuated to circuit closing position by the circuit closing movement of the switch, and a mechanical interlock between the switch and the actuating means for the circuit interrupter whereby when the switch is in circuit opening position the circuit interrupter 'actuating means is held against movement and the under-current armature is retained in attracted position, and said auxiliary contacts in circuit closing position maintaining the electromag'net energized after the initial energization or the electromagnet.

9. A circuit protecting device comprising a coil connected in the circuit to be protected and having a core arranged with a bore of different diameters 'at the opposite end portions, an overcurrent plunger reciprocable axially in the portion of largest diameter of the bore of the coil core and adapted to be moved to an attracted position upon occurrence of over-current conditions in said circuit, an under-current armature pivotally mounted at one end of the coil and yieldi'ngly urged to move to a non-attracted position upon occurrence of under-current conditions in said circuit, and an actuating rod having a head at one end and slidably mounted in the bore portion of smallest diameter of the coil core above the over-current plunger and adapted to be lifted by the movement of the over-current plunger to attracted position and passing through an opening in said under-current armature with the head resting on said under-current armature whereby the rod is lifted by the under-current armature assuming non-'attracted position.

l0. A circuit protecting device as claimed in claim 9, a ring of non-magnetic material fitted on the over-current plunger to prevent sticking of said plunger in the core.

ll. A circuit protecting device comprising a coil connected in the circuit to be protected and having a core arranged with a bore of different diameters at the opposite end portions, an overcurrent plunger reciprocable axially in the bore portion of largest diameter of the coil core and adapted to be moved to an attracted position upon occurrence of over-current conditions in said circuit, a fixed plate extending alongside of said coil, an under-current armature pivotally mounted on said iXed plate at one end of the coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in the circuit, an actuating rod having a head at one end and slidably mounted in the bore portion of smallest diameter of the coil core above the overcurrent plunger and adapted to be lifted by the movement of the over-current plunger to attracted position and passing through an opening in the under-current armature with the head resting on the under-current armature whereby movement of the under-current armature will lift the actuating rod, and said core, fixed plate and under-current armature forming a magnetic circuit.

12. A circuit protecting device comprising a coil connected in the circuit to be protected and having a core arranged with a bore of two diameters at the opposite end portions, an overcurrent plunger reciprocable ax'ally in the bore portion of largest diameter of the coil core and adapted to be moved to an attracted position upon occurrence of over-current conditions in the circuit, an under-current armature comprising a bifurcated plate pivotally mounted at one end of said coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in the circuit, an actuating rod having a head at one end and slidably mounted in the bore portion of smallest diameter of the coil core above the over-current plunger and adapted to be lifted by the movement of the over-current plunger to attracted position and passing through the bifurcation of the under-current armature plate at right angles to its pivotal axis with the head resting on the under-current armature plate whereby the rod is lifted by the movement of the under-current armature plate to non-attracted position, and a silencing coil mounted upon one of the bifurcation legs of the under-current armature plate.

having a core arranged with a bore of different .diameters at the opposite end portions, an overcurrent plunger reciprocable axially in the bore portion of greatest diameter of the coil core and adapted to be moved to an attracted position upon occurrence of over-current conditions in said circuit, an under-current armature pivotally mounted at one end of the coil and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in said circuit, a switch having its contacts connected in the circuit to be protected, an electromagnet connec-ted in the circuit to be protected and having a movable core connected to the switch to close the switch upon energization of the electromagnet and open the switch upon de-energization of the electromagnet, an actuating rod having a head at one end and slidable in the bore portion of smallest diameter of the coil core above the over-cure rent plunger and adapted to be lifted by the movement of the over-current plunger to attracted position and passing through an opening in the under-current armature with the head resting on the under-current armature whereby the rod is lifted by the movement of the under-current armature to non-attracted position, auxiliary maintaining contacts connected in the circuit of the electromagnet and yieldingly urged to circuit opening position and actuated to circuit closing position by the movement of the electromagnetically actuated switch to circuit closing position, a mechanical interlock extending between the electromagneticallyactuated switch and the actuating rod and yieldingly' urged to hold the rod against movement when lthe electromagnet is deenergized despite the de-energizitio-n or the ccil, and the auxiliary contacts maintaining the energization of the electrcmagnet after the initial energization of the electromagnet.

14. A circuit protecting device for a three phase alternating current circuit comprising three coils connected respectively in the three phases, overcurrent armatures' associated respectively with said coils and adapted to move to an attracted position upon occurrence of over-current conditions in the respective phases, under-current armatures associated respectively with said coils and yieldingly urged to a non-attracted position upon occurrence of under-current conditions in the respective phases, a three pole switch having its contacts connected in the three phases, an electromagnet connected in the circuit of two of the three phases and having a movable core member connected to the movable contact makers of the three pole switch and adapted upon de-encrgization of the el-ectromagnet to effect opening of said switch, a circuit interruptor connected in the circuit of the electromagnet and normally in circuit closing position, a member extending relative to the three coils and adapted to actuate the circuit interrupter to circuit opening position by the movement of any one of the over-current armatures to its attracted position and by the movement of any one or the under-current armatures to its non-attracted position, and a mechanical interlock extending between the electromagnetically actuated switch and said member and yieldingly urged to engage said member and hold the under-current armatures in attracted position when the electromagnetically actuated switch is in circuit opening position.

15. An electric circuit protecting device adapted to be interposed in the circuit to be protected, comprising switch means connected in the circuit to be protected normally assuming circuit opening. position, electromagnetically operated means connected in a local electric energizing circuit adapted upon closing of said local circuit to energize the same and actuate said switch means to circuit closing position and connect the electromagnetically operated means in and maintain said circuit to be protected closed, a circuit in- -terrupter interposed in the local circuit of the electro-magnetically operated means and normally urged to circuit closing position, means operative to actuate said circuit interrupter to circuit opening position, a coil connected in the circuit to be protected, an armature movable into and outwardly of one end of said coil and normally assuming a position outwardly of the coil, said armature upon an occurrence of an over-current condition in the circuit to be protected being attracted to and movable into the coil to operate the interrupter actuating means to actuate the interruptor to circuit opening position, a second armature supported to have movement toward and away from the opposite end of the coil and yieldingly urged in a direction away from the coil to operate the circuit interrupter actuating means to actuate the circuit interruptor to circuit opening position and attracted to the coil upon the closing of the circuit to be protected 11 eind` energization of seidVv 0011,. and means auto?. maiieally operative 1190,11 the. opening of the Cire electromagntically operated switch actuating means to actuate the switch to circuit openingv position and engage the circuit interrupter :ictu-Y eting means and retain the second armature in its attracted position even though the coil as deenergized whereby the interruptor is in its normal circuit closing position when the electromeglo netically operated switch actuating means is deenergized and the. switch is in circuit opening position.

FREDERICK. JAMES EAYI'IT- uit to be protected and cie-,energizing of the*l REFERENCES CITED The following reterenees are Qf resend inthe. le of this.. petentr 

